Many trees do not grow straight so that the logs cut from the trees are swept or curved in shape. Special procedures and equipment must be used to maximize the board feet of lumber cut from these imperfect logs. FIGS. 1A and 1B illustrate two typical swept or curved logs 2, 3. FIG. 2 is an end view of log 2 showing how the swept or curved feature is typically in a single plane. To create lumber from log 2, side boards 4, illustrated in FIG. 3, are, in this typical example, cut from log 2 by making cuts along lines 6, 7 on either side of log 2 so that each side board 4 has parallel, cut surfaces 8, 9 and unfinished, uncut edges 10, 11. These cuts are made in a conventional manner. What is left of log 2 is called a center cant illustrated as center cant 12 in FIG. 4.
Center cant 12 has opposite, parallel, cut surfaces 14, 15 which correspond to surfaces 9 of boards 4 made at cutting lines 7. The end 16 of center cant 12 in FIG. 4 has a number of dashed cut lines 18 corresponding to where cant 12 will be rip sawn to create center cant lumber 20. See also FIG. 5. To maximize the board feet of lumber from center cant 12, cut lines basically parallel the edges 22 of center cant 12. While the center cant lumber 20 will originally have the same curved or swept shape as center cant 12, most, if not all, of this curve can be removed during drying operations. Side boards 4 are cut differently than center cant 12 to maximize the amount of side board lumber 24 as suggested in FIG. 6. Using conventional computer-controlled edger optimizing systems, the number, size and position of center cant lumber 20 and side board lumber 24 are determined automatically using appropriate computer programs based upon profile information of the side board 4 or center cant 12 scanned into the computer.
For example, U.S. Pat. No. 4,239,072 discloses a method and apparatus for edge trimming a side board. A number of overhead pressure rolls engage the side board as the side board passes along a chain conveyor. The side board is centered by sets of centering rolls. A number of scanning gates are positioned above the conveyor to provide a computer with appropriate information on the profile of the side board. The edging assembly includes a pair of adjustable cutting heads designed to chip the unwanted edges from the side board. The cutting heads are slewed in a direction perpendicular to the direction of movement of the board by hydraulic cylinders so that one or more pieces of side board lumber can be cut from a single side board.
U.S. Pat. No. 4,449,557, assigned to the same assignee as U.S. Pat. No. 4,239,072, uses substantially the same system for delivering partially cut logs to an edging assembly as the '072 patent. However, instead of using angled edge chippers, as in the '072 patent, the '557 patent uses sawing disks or saw blades to make the edge cuts. The entire edger saw system moves as a unit so that the sawing disks can skew, that is change the angle between the axis of rotation of the sawing disks and the direction of feed of the work piece and can slew, that is move laterally along a line generally perpendicular to the direction of feed of the work piece.
Some conventional edger optimizer systems measure the boards transversely and then position the board onto a feeding mechanism and move the board longitudinally into the edger. This conventional method requires a considerable amount of expensive scanning, positioning and transporting equipment to carry out the process. Conventional systems also commonly create cumulative scanning, positioning and transport errors that make the systems somewhat less than optimal. With regard to the '557 patent, complex board centering mechanisms, multiple scanner heads, complex and high maintenance feeding and tracking devices, and complex high inertia edger rotation devices are all characteristic of the system described in the patent.
U.S. Pat. No. 5,761,979 and U.S. Pat. No. 5,870,939 describe a saw assembly that includes a rotatable arbor on which two or more saw blades are mounted. The driving interface between the saw blades and the arbor permits the axis of rotation of the saw blades to be collinear with the arbor axis or skewed a few degrees in either direction. A saw blade positioning assembly includes pairs of guide arms which engage the sides of the saw blades to position each saw blade at the proper location along the arbor and at the proper skew angle. The guide arms are moved in unison so that the axial position and the skew angle of each of the saw blades can be changed in unison before and during sawing operations.
In these designs, the use of guide arms that engage the sides of the rotating saw blades, require constant maintenance and can often lead to problems. These saw guide arms require the use of saw blade lubricants and cooling water that reduce the fuel value of the saw dust and cause environmental and waste water concerns.